[s10e6] Extremis Now

The episode's central mystery involves the , an ancient text in the Vatican's secret library that causes anyone who reads it to commit suicide.

Upon realizing he is a "simulacrum," the virtual Doctor uses his sonic sunglasses to record the entire experience and emails it to the real Doctor in the physical world as a warning of the impending invasion. The Vault & Missy [S10E6] Extremis

The Doctor (Peter Capaldi) discovers that the "real world" he is in is actually an incredibly detailed computer simulation created by an alien race known as the Monks. The episode's central mystery involves the , an

The Doctor Who episode is a mind-bending sci-fi thriller written by Steven Moffat that serves as the first part of the "Monks" trilogy. It is widely acclaimed for its complex "simulation theory" plot and for finally revealing the contents of the vault. The Simulation Reveal The Doctor Who episode is a mind-bending sci-fi

A series of flashbacks explains how the Doctor ended up guarding the mysterious vault under St. Luke's University: Doctor Who S10E6: Extremis - FilmInk

The simulation is so perfect that people only realize it is fake by attempting to generate random numbers; since computer code is pseudo-random, everyone in the simulation produces the same sequence.